Purpose of FND_REQUEST_SETS.CONCURRENT_PROGRAM_ID?

Recently we were experiencing an issue where an exception was occurring whenever users attempted to submit certain request sets via the Submit Request Set form.  The text of the exception states:

ORA-01403:
no data found

--------------------------------------------------------------

FRM-40735:
ON-INSERT trigger raised unhandled exception ORA-06503.

The strange thing was that by creating a whole new request set that exactly matched the existing request set we could successfully submit the request set.  After investigation, I found that the offending request sets all had an ID in the CONCURRENT_PROGRAM_ID column of FND_REQUEST_SETS.  By setting this column to NULL I could successfully execute the previously broken request sets.